1. Field of Invention
The present invention relates to a power amplifier. More particularly, the present invention relates to a power amplifier for amplifying an audio signal.
2. Description of Related Art
Many types of electronic audio amplifiers are used today for commercial public address systems, automobile stereo systems as well as portable battery operated products including two-way radios. These audio amplifiers have varying power requirements and amplification characteristics. One general type of audio amplifier is a Class D amplifier. Class D amplifiers exhibit a high efficiency and are commonly used with pulse width modulated (PWM) drivers. As is well known in the art, a class D audio power amplifier typically uses a complementary metal oxide semiconductor (CMOS) inverter whose logic state is switched depending on the PWM pulse.
Pulse width modulation (PWM), sometimes referred to as pulse duration modulation, is a signal processing technique in which a sample value of an input information signal is represented by some property of a resultant pulse other than an amplitude value. When PWM is used, the samples of a message are used to vary the duration of the individual pulses. Thus with PWM, input information is encoded into the time parameter instead of amplitude. The modulating input wave may vary the time of occurrence of the leading edge, trailing edge or both edges of the resultant pulse train.
However, when the audio power amplifier powers on, there might be a large dc current flowing into the amplifier and the load driven by the amplifier, which might damage the load and produce the unpleasant pop noise.
Hence, there is a need for a new audio power amplifier which can prevent the pop noise, and prevent the load from being damaged by the large dc current when the amplifier powers on.